This is a Program Project to continue investigation of the functions and trafficking of specific liver cell membrane proteins. Four projects involving 15 faculty investigators representing 6 academic departments are proposed. These projects share ideas, techniques, and investigators who meet often, both formally and informally. The proposed studies represent multidisciplinary approaches to several fundamental questions in liver pathobiology including mechanisms of trafficking of membrane proteins on specific cytoskeletal elements (Project 1), the regulation of expression and trafficking of connexins (Project 2), the identification of trafficking steps in endocytosis mutants (Project 3), and mechanisms of trafficking to autophagic vacuoles and lysosomes (Project 4). Project 4 is new and was added to the Program because of strong collaborations that developed with the existing three Projects. Major accomplishments over the past 5 year period include: (Project 1) reconstitution in vitro of the microtubule-based motility of early and late endocytic vesicles as well as exocytosing vesicles that contain Herpes simplex virus and identification of vesicle-associated motors and regulatory factors; (Project 2) identification and characterization of protein binding partners for connexin 32 that may regulate its trafficking to and from the plasma membrane; (Project 3) discovery that the association of a potential sorting heat shock protein heterocomplex with the phosphorylated asialoglycoprotein receptor cytoplasmic domain is mediated by a novel casein kinase 2 alpha subunit, CK2a. This Program also includes three Core facilities. The Administrative and Supporting Services Core (Core A) provides secretarial, bookkeeping, and common equipment functions. The Molecular Cytology Core (Core B) provides state-of-the-art microscopy and imaging services. A new Proteomics Core (Core C) has been added based upon the substantial use of this technology by each of the four Projects. All four Projects are concerned with interrelated areas of hepatocyte membrane biology and pathobiology, and each proposed project represents collaborative efforts between independent investigators. Collaborations within and between projects lead to extensions of an individual's expertise into important areas of liver pathobiology that could not otherwise be effectively investigated. The track record demonstrates the ability of the investigators involved to work together and interact synergistically within the framework of this Program to promote the sharing of ideas, methodology, and resources. Ultimately, the studies performed in this Program will lead to fundamental insights that should be important for understanding and treating or preventing various acquired and inherited disorders of the liver.